The present invention relates to a detection of a state of a coating film thickness on a surface of equipment and an object, such as a disk, used in ion implantation and the like. The present invention further relates to a method for detecting a state that a coating film on disk surface wears thin or a fact that potion at which the coating film has worn off. The present invention also relates to a monitoring of a thickness of a coating film on a disk surface.
In an ion implantation equipment, heretofore, an aluminum alloy having lightweight, excellent strength and good heat conductivity has used as a material for a disk 1 having a wafer 2 mounted thereon as shown in FIG. 1. However, in the case where the disk is produced with an aluminum alloy, there is the possibility that an alloy composition material including aluminum is sputtered with ion beams to contaminate a wafer. For thie reason, a method is employed in which a disk produced by an aluminum alloy is coated with a material such as silicon (Si) to reduce metal contamination from the disk.
However, a coating film on disk surface is gradually weared by sputtering with ion beam irradiation. When the wear reaches an aluminum alloy surface on the disk surface, metal contamination may generate. Therefore, in using a disk having a coating such as silicon on the surface thereof, it is necessary to detect a fact that a coating film on disk surface wears thin or wearing out, and to take a necessary action such as exchange of coating part, before the wear of the coating film reaches a limit.
Coating life could heretofore be predicted from a sputtering rate of coating material with implanted ion. However, implantation conditions (implanted ion species, energy, and implanted dose) vary depending on every ion implantation equipment, so that a life cannot be detected with good reliability with the conventional method. Further, a method of measuring a coating film thickness using a film thickness gauge or the like has a disadvantage that it takes much time for measurement.
A method of indirectly detecting a degree of wear of coating film thickness is not known in the conventional technique. However, according to Japanese Utility Model No. 2,573,028 by the present applicant, an ion implantation equipment was developed in which a table portion supporting a target material is provided on a disk mounting a wafer and the target material is fixed to the table portion, thereby reducing a charge amount of the target material loaded on the table portion with ion implantation.
This device can suppress charge-up with good efficiency by coating a plate of disk (disk cover) mounting a wafer with an appropriate material such as Si or SiC, and also can reduce contamination of a wafer or the like. Further, this device has a countermeasure that a potion to be coated is made small segments, so that coating can be conducted easily.
The present invention has been made in view of the above circumstances.
One object of the present invention is to provide a detection method of coating film that quickly detects a life of a coating film irradiated with ion beams to prevent a metal substance by sputtering from a surface and having a coating film formed thereon.
Another object of the present invention is to provide an ion implantation equipment using the detection method.
In order to achieve the above objects, the present invention has the following embodiments.
A first aspect of the present invention relates to a detection method of a coating film thickness, which comprises providing an electrical measurement sensor having a coating film comprising a low conductive material on a surface of an object having the same coating film formed thereon, and detecting a thickness change of the coating film on the surface of the object by referring to a value of the signal from the sensor when a particle beam irradiates the surface of the sensor and the object.
According to the above structure, because the electrical measurement sensor and the object are coated with the film of the same material, film thickness change on the surface of the object can be detected through a signal from the sensor obtained by film thickness change of the coating film of the electrical measurement sensor.
A second aspect of the present invention relates to a detection method of a coating film, which comprises the steps of providing an electrical measurement sensor on the surface of a disk which includes a sample piece covered with a coating film comprising the same material formed on a surface of the disk, detecting a change of electrical signals from the sensor when an ion beam irradiates the sample piece during ion implantation, and converting the voltages of the sensor signals to the amount of decrease of the coating film thickness of the disk surface.
According to the above structure, the sample piece of the electrical measurement sensor wears thin with wear of the coating film in the same rate as in the disk, and the degree of wear of the coating film on the disk surface can be detected from a sensor signal from the sample piece.
According to the second aspect of the present invention, the method comprises detecting, as a change of sensor signal, a change of a charge amount due to flowing a material having electric charge into the sample piece of the electrical measurement sensor, and measuring the change of film thickness of the coating material based on this change detecting a change of electrical signals from the sensor when an ion beam irradiates the sample piece during ion implantation, and converting the voltages of the sensor signals to the degree of decrease of the coating film thickness of the disk surface.
According to the above structure, the change of film thickness of the coat film of the sample piece is approximately proportional to the change of the charge amount by charged particles of ions or electrons by ion beams flowing into the sample piece, so that this makes it possible to detect the degree of wear of the coating film on the disk surface from the charge amount of the sample piece.
According to the second aspect of the present invention, the method comprises further step of providing a reference sensor placed on the disk apart from the wafer, which consists of the same material as the disk and has the same area exposed to ion the beam as the sensor but has no coating film, and detecting a time when the sensor signal by electrical measurement sensor having the coating film consists with the reference value of a sensor signal obtained from the reference value sensor.
According to the above structure, the signal from the reference sensor with no coating material of the same material as the disk can be compared with the sensor signal from the electrical measurement sensor at the time when the coating film of the electrical measurement sensor wears and the surface of the same material as the disk is exposed, and when two sensor signals are of equal value, it is possible to detect that the coating film thickness on the disk surface has worn out.
A third aspect of the present invention relates to an ion implantation equipment comprising an electrical measurement sensor provided on a disk and having a sample piece covered with a coating film of the same material as that of a surface coating of the disk, and means to monitor thickness change of the coating film by sensor signal from the measurement sensor.
According to the above structure, the wear state of the coating film of the disk is detected as sensor signal from the sample piece of the electrical measurement sensor.
According to the third aspect of the present invention, the degree of wear of the coating film thickness of the electrical measurement sensor can be determined by a control unit.
According to the third aspect of the present invention, ion beams are scanned uniformly and around disk periphery relative to the wafer surface by the rotational and reciprocal movement of the disk. Therefore, if at least one electrical measurement sensor is arranged between wafers, the same thickness change of the coating film as that of the disk surface is obtained in the range of beam irradiation region.
According to the third aspect of the present invention, the coating film thickness of the sample piece is the same or slightly smaller than that of the disk. As a result, the remaining thickness of the coating film of the sample piece can be the same as or slightly smaller than that of the disk surface.
According to the third aspect of the present invention, film thickness change of the electrical measurement sensor is detected as the change of the sensor signal voltage generated relative to ground potential. Therefore, change of the coating film can easily be detected by measuring equipment such as a voltage indicator.
According to the third aspect of the present invention, because the coating face of the electrical measurement sensor is arranged at a position higher or lower than that of the disk, the sample piece of the sensor does not receive influence of sputtering from the disk face. Further, if the disk and each coating film of the sensor are arranged at the same plane, the irradiation conditions of ion beams are the same. As a result, the coating film thickness varies in the same proportion, and detection accuracy can further be improved.
According to the third aspect of the present invention, because the coating face of the electrical measurement sensor is arranged at a position higher or lower than the position of the disk, the sample piece of the sensor does not receive influence of sputtering from the disk face. Further, if the disk and each coating film of the sensor are arranged at the same plane, the irradiation conditions of ion beams are the same. As a result, the coating film thickness varies in the same proportion, and detection accuracy can further be improved.
According to the third aspect of the present invention, because the reference sensor having a small detection face of the same material as in the disk face not coated with coating film, thickness change of the coating film can be detected by comparing each sensor signal of the electrical measurement sensor and the reference sensor.